The hydraulic trim-tilt system disclosed in allowed U.S. patent application Ser. No. 06/191,733 by the present inventor provides a trim-tilt system for outboard propulsion units which uses a pilot valve in the trim piston to provide a different operating pressure for the tilt and trim ranges of operation. In that system it was observed by the inventor that when trimming the propulsion unit in, i.e., downward, the propulsion unit would occasionally continue to move in after the pump was stopped. The continuing movement thus resulted in imprecise trim settings when trimming in, particularly when the unit was lightly loaded as when the drive unit was operating at low power settings or idling.
Another hydraulic trim-tilt system using a shuttle valve to control flow from a pump to hydraulic cylinders is disclosed in U.S. Pat. No. 3,885,517 to Borst, et al.